Plasma processing apparatus

ABSTRACT

A plasma processing apparatus capable of extending a period of maintenance and continuing stable processing is provided. The apparatus comprises a vacuum reactor  1  having a processing gas introduction device and a evacuating device, a shield electrode  14  formed on the outer circumferential wall of the vacuum reactor, and a specimen placing device  101  having an antenna electrode  51  for radiating high frequency power into the vacuum reactor, in which first high frequency power is supplied to the antenna electrode, and high frequency power at a frequency lower than that of the first high frequency power is supplied to the antenna electrode  51  and the shield electrode  15.

BACKGROUND OF THE INVENTION

The present invention relates to plasma processing apparatuses and,particularly, it relates to a plasma processing apparatus capable ofconducting stable processing.

In recent years, miniaturization and high-integration for semiconductordevices such as ULSI (Ultra Large Scale Integration) have beenprogressed rapidly, and devices with fabrication size of 0.13 μm willsoon be put into mass production and devices of 0.1 μm size have nowbeen also under development. In addition, improvement in the operationspeed of LSI has been progressed rapidly and Cu wiring and lowdielectric constant films have now been used for decreasing wiringdelay. Further, the structures of devices have also been complicated andkinds of films to be used have become more versatile.

Further, to increase the number of chips obtainable per one wafer sheet,it is necessary to constitute a production line capable of handlingwafers of large diameters such as 300 mm. This has demanded higheraccuracy and applicability to larger diameters in etching techniques. Inparticular, in etching oxide films, it is necessary to form contactholes for wiring, fabricate organic or inorganic low dielectric constantfilms for forming damascenes and, further, fabricate various masks,which increases the number of steps.

As the device size is reduced to about 0.1 μm, dimensional fabricationaccuracy at the nanolevel in view of a CD (Critical Dimension) value isdemanded. Further, in etching, when it is intended to obtain a high etchselectivity to the underlying film or the resist film, “etch stop” inwhich an etching reaction is stopped in the course of processing or “RIE(Reactive Ion Etching-Lag)” in which an etching rate differs dependingon the bore diameter to be fabricated (to be etched) is liable to occur.That is, it is difficult to provide compatibility between the aspectvertical fabrication and high selectivity. Further, as the kind of filmsto be fabricated differs, the processing gas also varies, anddistribution of plasmas or radicals in the processing chamber alsovaries in accordance therewith. Therefore, control means for plasmas orradicals is also important.

In addition to the problems described above in view of the performance,it has also been demanded for the suppression of formation of obstaclescaused by deposition of fluorocarbon gases or radicals used uponprocessing for example to the inner wall of the processing chamber, orcountermeasure for reducing the exchange cost of consumed parts such assilicon plates constituting the inner wall of the processing chamber.

JP-A No. 8-339984 discloses a parallel plate type plasma processingapparatus, which applies two different RF (Radio Frequency) voltages toopposing electrodes when processing insulative films by utilizingplasma. In this apparatus, an upper electrode and a lower electrode arevertically disposed oppositely to each other in the processing chamber,radio frequency power is supplied to at least one of the upper and lowerelectrodes to ionize and dissociate processing gases introduced into theprocessing chamber and wafers are processed by using resultant ions orradicals.

JP-A No. 8-288096 discloses a plasma processing apparatus comprising anupper electrode made of a silicon plate formed with a gas hole forintroducing gas into a processing chamber and a permanent magnetdisposed in a ring-like configuration on the back of the upperelectrode.

JP-A No. 2000-36484 discloses a plasma processing apparatus forfabrication of organic low dielectric constant films, in which radiofrequency waves at 13.56 MHz are supplied to a lower electrode, coilsare disposed on the periphery of the processing chamber and radiofrequency waves at 13.56 MHz are supplied to the coils, and in whichelectrostatic shields are disposed between the coils and a dielectricwall for preventing consumption of the dielectric walls.

Further, Manual for RIE apparatus Exelan 2300 manufactured by LamResearch Corp. discloses a plasma processing apparatus in which highfrequency waves at two kinds of frequencies (2 MHz, 27.12 MHz) areapplied to an electrode mounting a workpiece to be processed thereon togenerate plasma from the wafer mounting side, so that the voltage is notapplied to a silicon plate disposed on the surface opposing to thewafer, thereby preventing consumption of the silicon plate.

In the apparatus of JP-A No. 8-339984, along with increase in the highfrequency to be used, high frequency waves penetrate between the upperelectrode and a cooling metal plate or in a discharge port (gas blowingport). Since the depth of penetration is extremely thin (1 mm or less),a high electric field is applied to the penetration portion tending tocause abnormal discharge. Once abnormal discharge occurs, the diameterof the blowing port is enlarged to generate plasma even further inside,causing formation of obstacles. In addition, since the potential on theupper electrode is naturally increased by the high frequency waves, theelectrode is scraped by sputtering plasma. This may sometimes increasethe frequency of exchanging Si upper electrodes, which are expensiveconsumption parts.

In the apparatus of JP-A 8-288096, magnetic fields are locally formed ata restricted portion having the size substantially equal to that of thepermanent magnet. When it is intended to increase the confinement effectby the magnetic fields, the magnetic fields near the permanent magnetsare increased in strength partially to thereby increase the plasmadensity at this portion. Further, since bias is applied to the RFelectrode to draw ions in the plasma, sputtering occurs locally. Thisresults in local consumption of the electrode to sometimes increase theamount of obstacles formed and lower the reliability of the apparatus.

In the apparatus of JP-A 2000-36484, the coils are wound around thelateral side of the processing chamber and plasma is generated byinduction coupling. In this case, scraping of the local wall in theprocessing chamber caused by the increase in the voltage applied to thecoils is prevented by electrostatic shields (Faraday shields).Accordingly, the shielding effect is not uniform between the openingsand portions other than the openings of the electrostatic shields.Further, plasma ignitionability is sometimes degraded.

In the apparatus of Manual for RIE apparatus Exelan 2300 manufactured byLam Research Corp., since two kinds of higher and lower high frequencywaves are supplied from the wafer to generate high density plasma on theside of the wafer, the increase of the etching rate can be expected. Onthe other hand, since the plasma or radicals prevail also to the surfaceopposing to the wafer mounting surface, they attack also the opposingwalls (or silicon substrate surface). Accordingly, scraping or filmdeposition occurs on the opposed surface.

Further, since ions are incident on the wall due to the potentialdifference between the plasmas and the wall, the plasma potentialfluctuates in accordance with the potential on the side of the lowerfrequency supplied from the wafer mounting electrode. Further, sinceions are incident on the wall due to the potential difference betweenthe plasmas and the wall, it is difficult to control the energy of theions incident on the wall independently of the wafer potential.Accordingly, it is sometimes difficult to control the scraping of thewall or deposition.

As described above, in the parallel plate type plasma processingapparatus, the voltage on the electrode itself applied with the highfrequency sometimes becomes high. Further, in the apparatus ofgenerating plasma from the wafer mounting electrode, a ground electrodeis etched due to the difference between the potential of the counterelectrode serving as the ground and the plasma potential.

A silicon plate is used for the counter electrode formed on the surfaceopposing to the wafer with a view point of generation of obstacles orwith a view point of scavenging F (fluorine) radicals (F radicals in thegas phase are adsorbed to Si in the form of SiFx to decrease). In thiscase, the silicon substrate is consumed at an early stage. Since thesilicon substrate is expensive, reduction in the amount of consumptionof the silicon plate is necessary also with a view point of reducing themanufacturing cost.

SUMMARY OF THE INVENTION

In view of the foregoing problems, the present invention has been madeand it is an object of the present invention to provide a plasmaprocessing apparatus capable of continuing stable processing with aperiod of maintenance extended.

In accordance with the present invention, the following means areadopted in order to solve the foregoing problems.

In accordance with an aspect of the present invention, there is provideda plasma processing apparatus comprising a vacuum reactor havingprocessing gas introduction means and evacuation means, a shieldelectrode formed on the side of the outer circumferential wall of thevacuum reactor, and a specimen placing device having an antennaelectrode for radiating high frequency electric power into the vacuumreactor, wherein first high frequency power is supplied to the antennaelectrode, and high frequency electric power at a frequency lower thanthat of the first high frequency electric power is supplied to theantenna electrode and the shield electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent fromthe following description of embodiments with reference to theaccompanying drawings in which:

FIG. 1 is a view for explaining a plasma processing apparatus accordingto a preferred embodiment of the present invention;

FIG. 2 is a view for explaining another embodiment of the invention;

FIG. 3 is a view for explaining a further embodiment of the invention;

FIG. 4 is a view for explaining a still further embodiment of theinvention; and

FIG. 5 is a view for explaining a still further embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is to be described by way of preferred embodimentswith reference to the accompanying drawings. FIG. 1 is a view forexplaining a plasma processing apparatus according to a preferredembodiment of the present invention. A vacuum reactor 1 constituting theplasma processing apparatus has a wall of a dielectric body 14 such asmade of quartz at the inside thereof to form a processing chamber 2.Further, an antenna electrode 51 and a specimen bench 5 for placing aspecimen (wafer) 4 as an object to be processed are provided inside theprocessing chamber 2. A processing gas is introduced from an upper partof the processing chamber 2 and the introduced processing gas 3 isexhausted by an exhaustion system 6. A suscepter 7 is disposed on theouter circumference of the wafer processing surface of the specimenbench 5. A first high frequency (UHF or VHF) power source 8 used forgenerating plasma and a second high frequency power source at afrequency lower than that of the first high frequency power source 8 foruse in drawing ions are supplied to the antenna electrode 51.

The first high frequency power source 8 and the second high frequencypower source 9 are supplied respectively by way of a coaxial wave guidechannel 10 to the specimen bench 5 and the antenna electrode 51. Adielectric body 12 is filled between the specimen bench 5 and a metalwall 11 to electrically insulate them from each other. Further, thespecimen bench 5 has a cooling device 13 and the temperature of thespecimen bench 5 can be controlled by allowing coolant to flow in thecooling device 13. A second electrode (shield electrode) 15 is disposedon the outside of the dielectric body 14 constituting the processingchamber 2. In addition, a third high frequency power source 16 isconnected to the shield electrode 15. The third high frequency powersource 16 may be at a frequency equal to that of the second highfrequency power source.

Wafer processing by using the plasma processing apparatus is to bedescribed by way of example of etching an oxide film. First, thespecimen 4 is conveyed by a conveying device not shown onto the antennaelectrode 51 in the processing chamber 2. A processing gas 3 comprising,for example, fluorocarbon gas, O₂ and Ar is introduced into theprocessing chamber 2 and, after setting the pressure in the processingchamber 2 to a predetermined value, electric power of the first highfrequency power source 8 is supplied by way of the coaxial wave guidechannel 10 to the antenna electrode 51. The first high frequency powersource 8 is passed through the dielectric body 12 and radiated by way ofthe suscepter 7 into the processing chamber 2 to generate plasma in theprocessing chamber 2.

The processing gas is dissociated by the generation of the plasma toform fluorocarbon radicals CFx, CxFy or O, and the fluorocarbon radicalsare deposited on the wafer. In a case where the second high frequencypower source 9 is applied to the antenna electrode 51, a sheath isformed on the specimen 4, by which ions are incident on the fluorocarbonfilms deposited on the specimen 4, allowing etching to proceed. Reactiveproducts formed by the etching are deposited on the dielectric body 14as the wall of the processing chamber 2 like fluorocarbon radicals.

A second electrode 15 is disposed on the outside of the dielectric body14. By controlling the voltage applied to the electrode, the potentialon the surface of the dielectric body 14 can be set to a value slightlylower than the plasma potential. When the surface potential of thedielectric body 14 is set as described above, ions at low energy can beincident on the dielectric body 14. The incidence of the ions at lowenergy can suppress the reactive products or radicals from depositingonto the surface of the dielectric body 14. That is to say, when thesurface in the vacuum reactor is covered with the dielectric body 14 andfurther a voltage is applied to the second electrode 15 to apply theelectric field on the surface of the inner wall of the dielectric body14, deposition of the reaction products or the radicals on the innerwall can be prevented and the surface of the wall of the dielectric body14 is always refreshed, so that formation of obstacles can be suppressedeffectively.

FIG. 2 is a view explaining another embodiment of the invention. Asshown in the drawing, coils 17 are disposed on the outer circumferenceof the wall of a dielectric body 14 constituting a vacuum reactor of aplasma processing apparatus. A third high frequency power source 16 issupplied to the coils 17. The frequency of the third high frequencypower source 16 may be identical with that of the second high frequencypower. A metal Faraday shield 18 is disposed between the coils 17 andthe dielectric body 14 and on the upper surface of the wall of thedielectric body 14. A variable capacitor 19 or a variable inductor isconnected to the Faraday shield 18. The lateral surface 18 a of theFaraday shield 18 may be of a blind-like structure in which metalstripes and slits are arranged alternately. In addition, the ceilingpart 18 b of the Faraday shield 18 may be of a shape having an opening181 or a shape not having the opening 181. In the drawing, portionsidentical with those shown in FIG. 1 carry the same reference numeralsand the duplicate description is to be omitted.

During processing of the specimen by the generation of plasma,controlling the capacitance, for example, of the variable capacitor 19can control the voltage applied to the Faraday shield 18, with theresult that deposition of radicals or reactive products on the wall ofthe dielectric body 14 can be suppressed.

It is difficult to apply the shield voltage to the inner wall surface ofthe dielectric body 14 opposing to the opening portions of the Faradayshield 18. Then, when the Faraday shield 18 is rotated during processingof the specimen, to alternate the opening portions and the metalportions with each other, it is possible to prevent uneven scraping ofthe dielectric wall 14 or prevent uneven deposition of reactive productson the wall of the dielectric body 14.

Further, in a case where the ceiling part 18 b of the vacuum reactor iscompletely covered with the Faraday shield, standing waves at the TM01mode are sometimes formed in the plasma on the ceiling part, resultingin plasma density with the convex distribution. In such a case, it ispreferred to dispose the opening portion 181 or a recess 182 at thecenter of the Faraday shield 18 b.

FIGS. 3(a) and 3(b) are views for explaining a further embodiment of theinvention. FIG. 3(a) is a view showing an example in which the output ofthe second high frequency power source 9 shown in FIG. 1 is supplied byway of a power divider 20 and a phase shifter 21 to a second electrode(shield electrode) 15 and FIG. 3(b) is a view showing an example wherethe output of the second high frequency power source 9 shown in FIG. 2is supplied by way of a power divider 20 and a phase shifter 21 to thecoils 17. In the figures, portions identical with those shown in FIGS. 1and 2 carry the same reference numerals and the duplicate description isto be omitted.

As shown in FIGS. 3(a) and 3(b), the second high frequency wave sourceis supplied instead of the third high frequency wave 16 to the secondelectrode 15 or coils 17. The power divider 20 and the phase shifter 21divisionally apply the output of the second high frequency power sourceto the antenna electrode 51 and the second electrode 15. In addition,the ratio and the phase difference of the voltages applied to theantenna electrode 51 and the second electrode 15, or the antennaelectrode 51 and the coils 17 can be controlled by controlling the powerdivider 20 and the phase shifter 21.

This can control the voltage applied to the second electrode (shieldelectrode) 15 or the shield electrode 18.

For example, in a case where the phase difference between the voltage ofthe second high frequency power source 9 and the voltage of the shieldelectrode is 180°, the potential on the wall of the dielectric body 14is identical with the plasma potential when the specimen is drawing theions, and the plasmas no more hit on the wall. On the other hand, whenthe potential on the specimen becomes positive, the potential on thewall of the dielectric body 14 is lowered relatively to draw ions.

That is, deposition of films on the wall of the dielectric body 14 canbe suppressed by controlling the time for “deposition” and “removal” ofthe radicals or the reactive products on and from the wall of thedielectric body 14. When the phase difference is set to 0°, thedielectric wall 14 also draws ions when the ions are being drawn to thespecimen.

In a case of using a fluorocarbon gas as a processing gas, fluorocarbonradicals formed by dissociation are deposited on the specimen or thewall. Further, radicals are also formed from the fluorocarbon films uponincidence of ions. When the specimen 4 and the dielectric wall 14deflect at the same phase, the amount of the fluorocarbon in the plasmais increased more than that in the case of a phase difference of 180° (aloss is decreased). Accordingly, it is expected that the amount of theetchant will increase to improve the etching efficiency. While thedescription has been made of the case of the phase differences of 0° and180°, the voltage and the phase difference applied to the specimen 4 andthe dielectric wall 14 are preferably changed in accordance with thekind of the gas to be used and the amount of radicals or reactiveproducts to be formed.

FIG. 4 is a view explaining a further embodiment of the invention. In acase of using a high frequency power source at UHF or VHF as the firsthigh frequency power source 8, it may sometimes form a distinctly convexplasma distribution. This is because standing waves (TM01 mode) areformed in the sheath on the upper surface of the specimen 4.

Then, a disk-shaped cavity 22 is provided in the surface of the antennaelectrode 51. A dielectric body 23 may be filled in the cavity 22 forsuppressing electric discharge. The diameter of the cavity 22 is set toabout the distance between the nodes of the standing waves at the firsthigh frequency power source and the depth d is set such that theeffective distance d*=d/{square root}{square root over ( )}εγ (εγ:specific dielectric constant of the dielectric body) is approximatelythe thickness of the specimen to be used. This can generate uniformplasma and can uniformly apply the high frequency potential to thespecimen.

FIG. 5 is a view for explaining a further embodiment of the invention inwhich FIG. 5(a) is a view showing a plasma processing apparatus and FIG.5(b) is a view showing the bonding energy for the wall material and theradicals.

In this embodiment, the surface of the dielectric wall 14 is coated withthe flame-sprayed film of ZrO₂ or ZrO₂—Y₂O₃. Further, the surface of theground material 24 is also coated with the flame sprayed film of ZrO₂ orZrO₂—Y₂O₃. FIG. 5(b) shows calculated values for the bonding energy ofthe wall material and the radicals determined by a molecular orbitalmethod. A positive bonding energy shows that the radicals are adsorbedto the wall, while a negative bonding energy shows that they are notadsorbed, and the magnitude of the energy corresponds to the magnitudeof the adsorption force. SiO— shows that the wall material is made ofquartz and the adsorption side is O, while AlO shows alumina, and ZrO—shows zirconia.

Assuming a case of using aluminum-alumite coating for the groundmaterial, the following can be considered. Al, Al₂O₃ and F are reactedto form AlFx, which is released into the plasma. AlF₃, AlF₂ and AlF areadsorbed to the quartz of the wall with the bonding energy at 1.52 eV,5.58 eV and 3.49 eV, respectively. Further, when AlF is adsorbed furtheron AlF deposited on SiO, it is adsorbed weakly at the bonding energy of0.50 eV. On the other hand, SiF₄ as a typical reactive product formed byetching cannot be deposited on AlF. Weak bonding of AlF on AlF causes aproblem, in which Al is detached from quartz to form obstacles as theprocessing for the specimen proceeds.

Further, CF₂ as the etchant is bonded to AlO at 3.78 eV in which bondingenergy between Al and OCF₂ is as remarkably small as 0.71 eV. This showsthat incidence of ions extracts O from AlO (alumina: Al₂O₃) to causeetching.

On the other hand, in a case of ZrO₂, CF₂ is adsorbed (at 3.78 eV), inwhich the bonding energy between Zr—OCF₂ is as high as 1.78 eV, showingthat they are not etched easily by incidence of ions compared with thecase of aluminum or alumite. Also in the case of Y₂O₃, since O is notdetached easily by deposition of CFx, the surface of the compound may bestabilized also by adding Y₂O₃ to ZrO₂. While an example of coating thedielectric wall 14 with ZrO₂ is shown, only the ground material 24 maybe coated with ZrO₂ or ZrO₂—Y₂O₃ while leaving the dielectric of quartzas it is depending on the case.

As has been described above, according to each of the embodiments of theinvention, in the plasma processing apparatus of generating plasma byusing high frequency waves of VHF or UHF band, deposition of theradicals or the reaction products and sputtering by plasma can beprevented to decrease the cost of consumption components such as wallmaterials (COC) by controlling the potential or the phase thereof on thesurface of the dielectric as the wall. Further, no electrode is providedon the surface of the dielectric opposing to the antenna electrode.Accordingly, the potential on the wall surface can be optimized bycontrolling the potential of the shield electrode formed on the outercircumferential wall of the vacuum reactor. This can decrease theformation of obstacles from the wall, extending the period ofmaintenance.

As has been described above, the present invention can provide a plasmaprocessing apparatus capable of extending a period of maintenance andcontinuing stable processing.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

1. A plasma processing apparatus comprising: a vacuum reactor havingprocessing gas introduction means and evacuation means; a shieldelectrode formed on an outer circumferential wall of the vacuum reactor;and a specimen placing device having an antenna electrode for radiatinghigh frequency power into the vacuum reactor; wherein first highfrequency power is supplied to the antenna electrode, and high frequencypower at a frequency lower than that of the first high frequency poweris supplied to the antenna electrode and the shield electrode.
 2. Aplasma processing apparatus comprising: a vacuum reactor havingprocessing gas introduction means and evacuation means; a shieldelectrode formed on an outer circumferential wall of the vacuum reactor;a specimen placing device having an antenna electrode for radiating highfrequency power into the vacuum reactor; and an exciting coil formed onan outer circumference of an outer circumferential wall of the vacuumreactor; wherein a first high frequency power is supplied to the antennaelectrode, and high frequency power at a frequency lower than that ofthe first high frequency power is supplied to the antenna electrode andthe exciting coil, an impedance element is connected to the shieldelectrode, and a shield voltage is applied to the shield electrode byway of the exciting coil.
 3. A plasma processing apparatus according toclaim 2, wherein a slit is formed at a portion, of the shield electrode,facing the exciting coil in a direction substantially perpendicular tothe exciting coil.
 4. A plasma processing apparatus according to claim2, wherein a slit is formed at a portion, of the shield electrode,facing the exciting coil in a direction substantially perpendicular tothe exciting coil, and an opening or a dent is formed at a centralportion of the shield electrode on an upper surface of the vacuumreactor.
 5. A plasma processing apparatus according to claim 1, whereinthe antenna electrode and the shield electrode are connected by way of apower divider and a phase shifter.
 6. A plasma processing apparatusaccording to claim 2, wherein the antenna electrode and the excitingcoil are connected by way of a power divider and a phase shifter.
 7. Aplasma processing apparatus according to claim 1, wherein a disk-shapedcavity having a diameter corresponding to nodes of a standing waveformed on an upper surface of the specimen placed during plasmaprocessing is formed at a central part of the antenna electrode.
 8. Aplasma processing apparatus according to claim 2, wherein a disk-shapedcavity having a diameter corresponding to nodes of a standing waveformed on an upper surface of the specimen placed during plasmaprocessing is formed at a central part of the antenna electrode.
 9. Aplasma processing apparatus according to claim 1, wherein a disk-shapeddielectric layer having a diameter corresponding to nodes of a standingwave formed on an upper surface of the specimen placed during plasmaprocessing is formed at a central part of the antenna electrode.
 10. Aplasma processing apparatus according to claim 2, wherein a disk-shapeddielectric layer having a diameter corresponding to nodes of a standingwave formed on an upper surface of the specimen placed during plasmaprocessing is formed at a central part of the antenna electrode.
 11. Aplasma processing apparatus comprising: a vacuum reactor made ofdielectric having processing gas introduction means and evacuationmeans; a shield electrode formed on an outer circumferential wall of thevacuum reactor; a specimen placing device having an antenna electrodefor irradiating high frequency power into the vacuum reactor; and a ZrO₂flame-sprayed film formed on an inner wall surface of the vacuum reactormade of the dielectric; wherein first high frequency power is suppliedto the antenna electrode, and high frequency power at a frequency lowerthan that of the first high frequency power is supplied to the antennaelectrode and the shield electrode.
 12. A plasma processing apparatusaccording to claim 9 wherein a Y₂O₃ flame-sprayed film is provided on aninner wall surface of the vacuum reactor made of the dielectric.